1. Field of the Invention
The present invention relates to a fuel supply pump, and is suitable for application to, for example, a fuel supply pump, which pressure-feeds fuel under pressure equivalent to a fuel injection pressure in a fuel injection system of a diesel engine.
2. Description of Related Art
Conventionally, a pump which includes a cam that rotates upon application of driving force of an engine or the like, a plunger that reciprocates inside a pressurizing chamber, and a tappet that is provided between the cam and the plunger to convert rotary motion of the cam into rectilinear motion of the plunger, and which pressurizes fuel suctioned into the pressurizing chamber by the plunger that reciprocates as a result of the rotation of the cam, is known as a fuel supply pump (see, for example, JP-A-08-14140 corresponding to U.S. Pat. No. 5,603,303).
As a type of such a fuel supply pump, a device disclosed in JP-A-08-14140 includes a roller that rotates along a profile surface of a cam, a roller pin that rotatably supports a shaft of the roller from an inner side, and a tappet body having a supporting wall which has a cylindrical shape and supports both axial end parts of the roller pin, as components of a tappet. According to this technology, because the roller which is supported by the tappet body via the roller pin rotatably and slidingly contacts the cam, the roller mitigates sliding resistance of the cam and the tappet to enable smooth rotation-rectilinear motion conversion.
In a fuel supply pump as disclosed in JP-A-08-14140 above, which makes the tappet and plunger rectilinearly move as a result of the rotation of the cam and then pressure-feeds fuel in the pressurizing chamber by the plunger, when fuel is pressurized under pressure equivalent to injection pressure by pressure-feed movement of the plunger, reaction force caused by the fuel pressure is applied to the tappet, which supports the plunger, and the cam. In the tappet, which supports the roller via the roller pin against this reaction force, the reaction force applied to the roller and the tappet body needs to be supported by the axial end parts and the supporting wall of the roller pin.
However, according to the conventional technology of JP-A-08-14140, a pressure receiving width of the axial end parts and the supporting wall to which the above-described reaction force is applied is structurally limited to the supporting wall that is a side wall of the tappet body, which accommodates the roller, except the roller. In the conventional technology having such a structure, when the above injection pressure is more highly pressurized, a face pressure at the axial end parts of the roller pin exceeds a face pressure acceptable value, so that there is concern that damage such as seizure may be caused to the axial end parts.
Measures against the above concern may be that a pressure receiving area is increased so as to reduce the face pressure. However, a diameter of the roller pin is increased to a roller diameter or less, and even if the diameter of the roller pin is increased to the roller diameter, there is a limit to the increase in the pressure receiving area as a result of the product of the diameter of the roller pin and the pressure receiving width. In expanding the pressure receiving width, for example, because the tappet is upsized, there is concern that costs of the fuel supply pump may increase or installability of the pump in an engine may be limited.
Accordingly, the inventor considers directly supporting a roller by the above-described cylindrical tappet body. The following problems have been found out after the inventor conducts research in earnest. That is, it has been found that, although face pressure is reduced since an outer circumferential surface of a columnar roller is in sliding contact with a sliding contact surface of a tappet body, a corner portion of axial end part of the roller and a side wall of the cylindrical tappet body may be brought into contact with each other, thereby causing seizure. This is because at both axial end parts of the roller, a peripheral speed at the corner portion increases in accordance with the diameter expansion of the corner portion of the axial end part and furthermore, because contact pressure becomes high because of the contact of the corner portion with the side wall in a manner of line contact. Moreover, by reason of, for example, variation in alignment between the roller and the cam, force in a direction perpendicular to a direction of rectilinear motion of the tappet, i.e., in a thrust direction of the roller, is sometimes applied to the roller, so that there is concern that the above-described possibility may increase.